Current imaging devices such as Computer Automated Tomography (CAT) scanners typically use imager arrays in order to detect x-rays. A typical imager arrays generally consist of a matrix of picture element (pixel) sensors which employ photodetectors to detect the light emitted by a scintillation material, which has been excited by an x-ray, and a charge storage device (e.g., capacitor) to hold an amount of charge which depends on the intensity of the detected light.
In addition to the pixel elements in the imager arrays, other peripheral circuitry is typically used to access and read the charge held by individual capacitors. The other circuitry typically includes vertical and horizontal scanning circuits, amplifiers and switches. A major problem with this peripheral circuitry is that it consumes precious space on the imager arrays which could otherwise be used for light detection circuitry. The less light detection circuitry, the less accurate and precise are the detection readings. The space on the array which cannot detect light is known as dead space.
Examples of prior art imagers having dead space for the implementation of scanning circuitry include U.S. Pat. No. 5,184,018 (Conrads et al.) and U.S. Pat. No. 5,115,293 (Murayama et al.). Conrads discloses a light or x-ray sensitive sensor array in which each sensor has a photodetector in parallel with a storage capacitor which is serially connected with a switching FET. Conrads also discloses amplifiers, an analog multiplexer and a digital encoder all of which are separate from the sensor elements and implemented in the marginal area of the array. Murayama discloses an imaging device having a photodetector which is serially connected to two switching MOS transistors. Murayama also discloses a vertical scanning circuit and a horizontal scanning circuit separate from the pixel elements and implemented in the marginal area of the array.
In view of the disadvantages (e.g., increased size of the sensor) caused by dead space circuitry, it would be advantageous to have an imager array which provides, for example, amplifiers and scanning circuits but minimizes the amount of dead space on the array in order to maximize the accuracy and precision of the light detection readings. Substantially reduced dead space at the edges of an array also permit the arrays to be butted up against one another to form a larger array.